Recording of electrical impulses



Dec; 7', 1937. H, WEBER 2,101,419

RECORDING OF ELECTRICAL IMPULSES Filed July 25, 1956 Patented Dec. 7, 1937 UNITED STATES PATENT OFFICE Heinrich Weber, Berlin, Germany, assignor to Klangfilm G. m. b. H., Berlin, Germany, a corporation of Germany Application July 25, 1936, Serial No. 92,562 In Germany September 9, 1935 5 Claims.

This invention relates to the recording of electrical impulses such as those of audio frequency, and has for its principal object the provision of an improved apparatus and method of operation which have the advantage of simplicity and are easily controlled to record sound on a photographic film or the like.

Methods of producing noiseless talking films are known. In accordance with some of these methods, a part of the speech currents to be recorded is detected, and utilized for controlling an amplifier, or for directly displacing the zero line. In these arrangements, besides the detector, additional amplifier arrangements are required whereby the cost of the entire arrangement will be increased, and the apparatus becomes complicated. In accordance with other of these methods, the noise reduction biasing current is supplied directly to the recording element from the common lead between the plate and cathode of a push-pull connected Class B-operated amplifier such as those disclosed by Batsel and Belar application, Serial No. 651,738, filed June 14, 193 3 and Belar application, Serial No. 41,987, filed September 25, 1935. The present invention is similar to those of the aforesaid copending applications in that it involves the use of a Class B operated amplifier but differs therefrom with respect (1) to the details of the channel through which the noise reduction bias potential is applied to the recording element and (2) to the provision of an amplification control channel through which the grid bias of a leading amplifier stage is changed when the current of the common lead exceeds a predetermined value. This amplification control channel has the advantage that large amplitudes can be recorded in a comparatively weaker fashion than the smaller amplitudes.

As compared with the known methods, the method according to the invention has numerous advantages. It avoids necessity of detectors and additional amplifiers, the noise reduction control channel, and is thus especially suited for low-weight, transportable recording apparatus. Since such amplifiers are dispensed with, the entire arrangement becomes simpler, and assures a greater reliability of operation. Moreover, the invention provides advantages ordinarily assured by the application of a Class B-amplifier, such as high eificiency of the amplifier.

The invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope is indicated by the appended claims.

Referring to the drawing,

Fig. 1 is an explanatory diagram, and

Figs. 2 and 3 are wiring diagrams of recording systems connected in accordance with the invention. 5

Fig. 1 shows the circuit of a Class B-amplifier having the terminals K in the common plate circuit of both tubes. In a Class B-amplifier it is known that there flows between the said terminals K a direct current which varies approximately in 0 accordance with the alternating potential applied at E, as well as with that supplied by A. If the A. C. furnished by A operates a light-control organ, such as a recording galvanometer or light value, the variable D. C. appearing at K can be 15 used at the same time to control the noise reduction or bias current if suitable connections are provided at K. These connections may be so designed that the D. C. at K can be utilized directly for controlling the bias current. The D. C. at K may, however, furthermore be used for the control of an interposed amplifier stage.

Fig. 2 shows a circuit arrangement in which the D. C. appearing at the terminals K is furthermore used for controlling the degree of amplification of a preceding amplifier tube 8, such that the degree of amplification of this tube will be varied only from the moment at which the D. C. appearing at K exceeds a certain definite value. The terminals K are bridged by a condenser 9 forming a short circuit for the produced alternating potential. The condenser 4 is charged across valve 1 and resistor 2, and will be discharged across resistor 3 and recording organs. Through proper choice of resistors 2, 3 and of condenser 4, the time constant for charging and discharging of condenser 4 can be determined. Valve l prevents a discharge of condenser 4 across resistor 2 and resistor 5. There likewise passes a D. C. of the Class B-amplifier through the resistor I placed in the grid circuit of tube 8 in parallel to the bias battery 12, whereby said current produces a potential drop through resistor I. As long as this potential drop is lower than the voltage of battery l2, the bias of the amplifier tube 8 will not be changed. If, however, the D. C. of the B-amplifier becomes so high that the potential at resistor l exceeds the voltage of battery l2, the biasing potential of the amplifier tube 8 becomes higher so. that the amplification degree of the arrangement decreases. The variable resistor 6 is not always necessary. It may serve, however, for voltage division and may have the effect that the voltage at resistor 1 can be maintained lower than the voltage at resistor 5.

Fig. 3 shows a circuit arrangement in which the D. C. passing through the push-pull amplifier placed in the plate circuit, is utilized at the same time to vary the degree of amplification of the preceding tube 8. As regards charging and discharging of condenser s, as well as concerning the voltage at resistor 1 and the voltage division through resistor 6, the same is true as mentioned in connection with Fig. 2. The sole difference between the two circuits, according to Figs. 2 and 3, resides in that in Fig. 3, the resistor I is no longer in parallel to the biasing battery 12, but in series thereto. In this way it is accomplished that the variable D. C. of the B-amplifier aliects the biasing potential of tube 8 and hence its degree of amplification. The voltage drop through resistor 1, which is the greater the higher the alternating potential appearing at the terminals E (Fig. 1), increases the negative grid bias of tube 8 operating in the lower end of its characteristic, whereby at larger amplitudes said increase in negative grid bias is greater than at small amplitudes. The working point of the tube characteristic therefore will be displaced downwards, so that at recording of the respective sounds, the large amplitudes will be less amplified than the small amplitudes.

I claim as my invention:

1. A signal responsive apparatus including a pair of amplifiers connected in push-pull relation, means common to the grid circuits of said amplifiers for producing a control potential which varies in response to the signal to be amplified, a pair of leads associated with the output circuit of said push-pull amplifiers for delivering the amplified signal, a pair of leads common to the anode circuits of said amplifiers for producing a potential wl'L ch varies as the. envelope of said signal, and means associated with said common leads for controlling the input potential of said amplifiers only when said envelope potential exceeds a predetermined value.

2. A signal responsive apparatus including a pair of amplifiers connected in push-pull relation, means common to the grid circuits of said amplifiers for producing a control potential which varies in response to the signal to be amplified, a pair of leads associated with the output circuit of said push-pull amplifiers for delivering the amplified signal, a pair of leads common to the anode circuits of said amplifiers for producing a potential which varies as the envelope of said signal, means associated with said common leads for controlling the input potential of said amplifiers only when said envelope potential exceeds a predetermined value, a signal recorder, and means interposed between said common leads and said recorder for applying to said recorder a noise reduction bias potential which varies in accordance with said envelope potential.

3. A signal responsive apparatus including a pair of amplifiers connected in push-pull relation, means common to the grid circuits of said amplifiers for producing a control potential which varies in response to the signal to be amplified, a pair of leads associated with the output circuit of said push-pull amplifiers for delivering the amplified signal, a pair of leads common to the anode circuits of said amplifiers for producing a potential which varies as the envelope of said signal, means associated with said common leads for controlling the input potential of said amplifiers when said envelope potential exceeds a predetermined value, a recorder, and a channel including an asymmetric conductor, a pair of resistors and a capacitor connected in shunt to said resistors for applying to said recorder a noise reduction bias potential which varies in accordance with said envelope potential.

4. A signal responsive apparatus including a pair of amplifiers connected in push-pull relation, means common to the grid circuits of said amplifiers for producing a control potential which varies in response to the signal to be amplified, a pair of leads associated with the output circuit of said push-pull amplifiers for delivering the amplified signal, a pair of leads common to the anode circuits of said amplifiers for producing a potential which varies as the envelope of said signal, and m ans including a resistor connected across said common leads forrestricting the output of said amplifiers only when said envelope potential exceeds a predetermined value.

5. The combination of a pair of amplifiers connected in push-pull relation and biased substantially to cut oif, an amplifier provided with a signal input circuit and with an output circuit coupled to said push-pull amplifiers, a pair of leads common to the output circuits of said pushpull amplifiers for producing a potential which varies as the envelope of said signal, and means including an asymmetric conductor common to said leads and to said input circuit for controlling the input of said amplifier when said potential exceeds a predetermined value.

HEINRICH WEBER. 

